1. Field of the Invention
The present invention relates to a method and apparatus for providing electrical power when negative pressure is applied at a wound site. In particular, but not exclusively, the present invention relates to a method and apparatus for generating electrical power for a pump used to pump fluid from a cavity sealed over a wound site whereby power is generated using biological fluid collected from the wound site.
2. Description of the Related Art
There is much prior art available relating to the provision of apparatus and methods of use thereof for the application of topical negative pressure (TNP) therapy to wounds together with other therapeutic processes intended to enhance the effects of the TNP therapy. Examples of such prior art include those listed and briefly described below.
TNP therapy assists in the closure and healing of wounds by reducing tissue oedema; encouraging blood flow and granulation of tissue; removing excess exudates and may reduce bacterial load and thus, infection to the wound. Furthermore, TNP therapy permits less outside disturbance of the wound and promotes more rapid healing.
In International patent application, WO 2004/037334, apparatus, a wound dressing and a method for aspirating, irrigating and cleansing wounds are described. In very general terms, the application describes the treatment of a wound by the application of topical negative pressure (TNP) therapy for aspirating the wound together with the further provision of additional fluid for irrigating and/or cleansing the wound, which fluid, comprising both wound exudates and irrigation fluid, is then drawn off by the aspiration means and circulated through means for separating the beneficial materials therein from deleterious materials. The materials which are beneficial to wound healing are recirculated through the wound dressing and those materials deleterious to wound healing are discarded to a waste collection bag or vessel.
In International patent application, WO 2005/04670, apparatus, a wound dressing and a method for cleansing a wound using aspiration, irrigation and cleansing wounds are described. Again, in very general terms, the invention described in this document utilises similar apparatus to that in WO 2004/037334 with regard to the aspiration, irrigation and cleansing of the wound, however, it further includes the important additional step of providing heating means to control the temperature of that beneficial material being returned to the wound site/dressing so that it is at an optimum temperature, for example, to have the most efficacious therapeutic effect on the wound.
In International patent application, WO 2005/105180, apparatus and a method for the aspiration, irrigation and/or cleansing of wounds are described. Again, in very general terms, this document describes similar apparatus to the two previously mentioned documents hereinabove but with the additional step of providing means for the supply and application of physiologically active agents to the wound site/dressing to promote wound healing.
The content of the above-noted references is included herein by reference.
However, the above described apparatus and methods are generally only applicable to a patient when hospitalised as the apparatus used is complex, needing people having specialist knowledge in how to operate and maintain the apparatus, and also relatively heavy and bulky, not being adapted for easy mobility outside of a hospital environment by a patient, for example.
Some patients having relatively less severe wounds which do not require continuous hospitalisation, for example, but whom nevertheless would benefit from the prolonged application of TNP therapy, could be treated at home or at work subject to the availability of an easily portable and maintainable TNP therapy apparatus. To this end GB-A-2 307 180 describes a portable TNP therapy unit which may be carried by a patient and clipped to belt or harness. A negative pressure is applied at a wound site but that pressure is prone to fluctuation which may have a detrimental effect to healing.
In this and other portable devices which carry a suction pump, power is typically provided for the pump by a mains supply or by one or more batteries. When a mains supply is used the portability of the device is limited restricting movement of a patient. When one or more batteries are used a lifetime associated with the battery becomes a limitation on a length of time over which a topical negative pressure therapy unit can be used. Furthermore there is a concern on the mind of a user that a battery may be about to expire leaving therapy uncompleted. Still furthermore batteries are relatively heavy and costly which can inconvenience a user as well as a provider of the therapy units.
U.S. Pat. No. 6,294,281 discloses a fuel cell having an anode and a cathode which is capable of using compounds from biological systems as fuel for generating electrical power. However, the number of biological systems suggested is limited. Furthermore a pumping mechanism must be provided for pumping fluid of a biological system into the fuel cell.